Sound rerecording apparatus



Nov. 10, 1942. E. w. KELLOGG SOUND RERECORDING APPARATUS Filed Oct. 17, 194C mvenfor Patented NOV- 10, 1942 SOUND RERECORDING APPARATUS Edward W. Kellogg, Moorestown, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application October 17, 1940, Serial No. 361,559

9 Claims.

This invention relates to sound rerecording apparatus and more particularly to apparatus for rerecording sound from a plurality of lm sound are then combined into a single record which is photographically printed onto the combined sound and picture iilm. In the making cf this composite sound record, it is necessary to use ground noise reduction which may be accomplished in any of the ways customary in the art.

vvThe use of ground noise reduction in this apparatus involves a number of difficulties and most particularly those due to the time constants of the ground noise reduction circuits used.

It' has heretofore been proposed to use two reproducing systems in rerecording, one of these would provide the impulses to operate the ground noise reduction ampliiier and the second one spaced therefrom along the lm bysuch a distance as to provide a sufficient amount of anticipation would provide the sound pickup to be amplified and transmitted to the recorder. With this arrangement the sound impulses from the rst pickup would be amplified and rectied and transmitted to the ground noise reduction appa- .ratus of the recorder enough in advance of the arrival of the sound impulses so that no clipping of the peaks would occur on a sudden increase in the sound.

The advantages to be gained vby the employment of the anticipating pickup, are important and well worthwhile, but in view of the lcommon practice already mentioned, of mixing the outputs of a number of reproducing machines together to provide the signal to be recorded, the provision of a satisfactory anticipating signal involves serious complexities in equipment. The advanced or anticipating signalshould be identical with the signal that is to be recorded, with the one dileren-ce that it is advanced in time. To provide such an advanced but identical signal, each reproducing machine must be provided with two pickup devices, all of the ampliers must be duplicated, and all of the mixers must be in duplicate with mechanical interconnection of (Cl. Uil-100.3)

controls, so that the movement of any control knob causes an identical change in the level of both the main and the advance signal as received from the main and the advance pickups of each reproducing machine.

' This complication of equipment and the numerous equalizing adjustments, which would be required, have been serious enough to prevent the adoption of the anticipating pickup system. Accordingly, it is the purpose of my invention to provide a simpler system which will afford practically all of the benet to be had from a complete system as described above.

Although the rerecording systems employed in motion picture studios employ a large number of synchronously operated reproducing machines, each contributing some selected sound to the nal record, it is nevertheless true that one single machine contributes by far the largest `part of the sound, namely in most motion picture productions, the main recently recorded dialogue Furthermore, it is speech sounds rather than music and other incidental sounds which derive the most benet from an anticipating system. The other sounds are usually subdued, as in music, or if mere noises are not seriously injured by clipping or momentary overloading due to failure of the ground noise system to be ready when a sudden increase in amplitude occurs. Thus if the benets of anticipation can be provided for that portion of the total recorded signal which is derived from a single machine, which carries the main dialogue original record, the remainder of the signals being handled as at present, nearly all of the actual benet of anticipation, in the way of an improved record, will be achieved. I therefore propose to provide only one (or at most a small fraction) of the reproducing machines with an extra pickup and to so design the ground noise reduction system that the advance pickup signal provides anticipation for all of the sound derived from the record played in the machine so equipped, without impairing the action of the ground noise reduction system in relation to all other sounds.

In the apparatus of the present invention I have provided an improved type of anticipating reproducer wherein the shutter of the recorder is controlled either by the main signal or by the anticipating signal, whichever may be larger at any given instant. The main signal includes such incidental and background signals as are to be recorded, while anticipating the ground noise reduction circuit except when they occasionally exceed the main signal channel in amplitude. The

arrangement further is such that two or more reproducers of the anticipating type may be connected together in the same fashion and whichever reproducer provides the loudest signal will control the shutter opening during the time of that signal.

One object of the invention is to provide an improved sound reproducing apparatus.

Another object of the invention is to provide an improved rerecording apparatus.

Another object of the invention is to provide a rerecording apparatus for rerecording sound from a plurality of channels one of which controls the ground noise reduction apparatus of the recorder.

Another object of the invention is to provide a plurality of rerecording reproducers which will selectively control the ground noise reduction apparatus according to which one produces the signal impulses of the greatest amplitude.

Other and incidental objects or" the invention will be apparent to those skilled in the art from a reading of the following specification and inspection of the accompanying drawing in which the single iigure is a schematic diagram of a rerecordingl channel made in accordance with the invention.

In the form of the invention shown in the drawing, the special reproducing channel `with the anticipating control of the shutter circuit is shown at the top of the figure, while the connections for the other reproducer channel and the recorder are indicated below. 1n the anticipating reproducer, a single exciter lamp lil may be used. The light therefrom may be directed by a condenser lens l! onto a slit plate l2 having two separated slits I3 and i4. VThe light from the slits is directed by the objective l5 upon the lrn F. The images of the slits I3 and i4 are sharply focused on the film where it passes through these beams carried on the surface of the drum I6. Light passing through the film is directed by the lenses il and I8 onto the photocells i9 and 2li.

It will be apparent that since the film moves .f

downwardly, any portion of the sound record will pass through'the beam from the slit |14 to the lens il and photocell i9 an appreciable instant of time before the other beam aiiects the photocell 2i?, and the relative timing of the impulses can be determined by the separation of the two beams on the film.

It will be apparent to those skilled in the art that the speciiic type of optical system and photooell arrangement shown is not essential to the operation of the device. For example, twoseparate exciter lamps and optical systems may be used, each operating independently of the other and with their images on the iilm spaced apart an appropriate distance. Aliso, instead of two separate photocells, a single photocell of the double cathode type may be used, either with the optical system shown or with the two independent optical systems. I

The output from the iirst photocell i8 is used exclusively for controlling the ground noise reduction shutter. In order to insure that the shutter and the recorded sound impulses will always have the proper relation, the output from the two photocells is directed through substantially identical channels as far as the main volume control, which precedes the recording ampliiier. From this point, theoutput from the two photocells is likewise directed through identical channels so that either the anticipating impulse or the later impulse will control the shutter, according to which is the larger.

The output from the photocell I9 is fed into the preamplifier 2l and similarly the output from the photocell 2e is fed into the preamplier 22. The output from these two preampliers is fed into the volume control 23 and the mixer 24, respectively. This volume control and the mixer control are mechanically interconnected so that any variation in one will cause a corresponding change in the other, thereby maintaining both outputs at the same level. The output from the volume control 23 is fed to the amplier and compressor 25 and the output from the mixer 24 is fed to the amplifier and compressor 26, these two elements being constructed with similar characteristics so that their effects on the two channels will be the same. tion of these ampliers and compressors is preferably made identical as nearly as is commercially convenient, and their characteristics may then be equalized by adjustment of appropriate circuit elements Vsuch as resistor or capacitors in the usual fashion.

rihe anticipating channel and theV reproducing channel are provided with the main volume controls 2l and 23, respectively, which are mechanically interconriectedso as toY maintain the level of the signals at this point the same in the two circuits. After passing these main volume controls, the audio frequency output in the main circuit is fed to the recording amplifier Mhwhich amplies the audio signals and transmits them to the recording galvanometer 4l. In the ground noise reduction channel, the output from the main reproducing photocell 29 passes "through the audio frequency stage of the ground noise reduction amplifier 3i) and the transformer 32 to the rectiiier 34. From this point on to the shutter this portion of the circuit is substantially the same as that which is used commercially. The rectified current is applied to the capacitor 35 shunted by the resistor 4l and passes through the resistor 35 to the capacitor 3l'. This resistorcapacitor network forms the usual iilter circuit and the output potential is applied to the grid of the ampliiier tube 33, the plate current of which passes through the winding 39 ofthe shutter, as indicated. It will be apparent that the main signal impulses thus will aifect theshutter at 39 in the usual manner. v

In the anticipating channel, the impulses pass through the audio frequency stage of the ground noise reduction amplifier 29 which is similar to i, the corresponding unit 3i! and through the transformer Sl to the rectifier y33. The output of the rectifier 33 is applied across the resistor 41 as indicated and aects the amplifying tube 38 in the same manner as the output of the rectifier 34.

It will be noted that the signal carried by the record F is employed twice in producing the total response of the ground noise reduction system, or the movement of the shutter 3S. On the other hand the signals from other records, which enter the system through connections 43 and 45 of the mixer affect the ground noise reduction system only once and thus do not have the benefit of any anticipation. t will be further noted, however, that the rectiiiers 33 and 34 through which the signals from the record F aifect the ground noise reduction system response, are connected in parallel, and it is well recognized that when rectiiers are so connected their voltages do not add, but that the rectified voltage depends only on the higher of the two input voltages. In

general, assuming that the two ampliiiersystems from photocells I9 and 20 respectively are adjusted for the same gain, about the only times when channel B will exceed channel A in output voltage will be during crescendos. At other times the rectied voltage and the response of the system as a whole will be the same as in a standard non-anticipating channel.

When a signal of high amplitude suddenly appears on the film F, it iirst affects the photocell i9 and the output from the rectifier 33 affects the tube 38 and the shutter 39 in sui'licient time so that in spite of time lag in the lter circuit 35, 36, 31 and the mechanical time lag of the shutter, the shutter will be opened sufficiently by the time the signal arrives through the recording channel 22, 24, 26, 40 so that there will be no clipping of the sound Wave images. Conversely, if a signal is maintained at a high amplitude and then suddenly stops, even though the impulse through the photocell I9 and rectier 33 has stopped an appreciable length of time before the signal applied to the recording galvanometer 4I, nevertheless, the signal will continue to be applied through the rectier 34 and the shutter will remain open, preventing clipping of the signal and causing the shutter to close after the cessation of the signal at a time determined by the constants of the iilter circuit 35, 36, 31, 41.

In this arrangement, the main sound record, which may include speech, singing or the like, is preferably reproduced through this reproducer equipped With the double pickup arrangement. Additional channels may be connected into the recording circuit through the mixer 24 through the circuits 43 and 45 controlled by the mixing controls 44` and 46. These additional channels which may provide musical background, sound effects or the like do not need to be connected to the anticipating rectier circuit, as an ordinary amount of clipping of the wave images of such sounds is ordinarily not noticeable and may be disregarded. These sounds, of course, control the ground noise reduction shutter through the rectifier 34.

If it is desired to provide additional channels having the anticipating feature described above in connection with the main channel, the anticipating circuits of these additional channels may be connected into the anticipating rectiiier circuit by substituting a mixer of the same general type as 24 for the volume control 23. Alternatively, any such additional anticipating circuits may be provided with similar and parallel amplier circuits corresponding to those of the oddnumbered elements of the figure and the output of that channel may be applied through a rectifier across the resistor 41.

It will be apparent to those skilled in the art that the use of the apparatus of this invention is not limited to its application to ground noise reduction systems, but the envelope voltage may be advantageously applied, for example, to the operation of such devices as automatic volume controls or compressors. l

Having now described my invention, I claim:

l. In combination' a plurality of electrical sound translating devices adapted to cooperate with a sound record in chronological sequence,

means for transferring impulses corresponding to sound Waves from one of said translating devices, means for independently deriving control currents corresponding to the envelope of sound impulses from both of said translating devices,

means for combining said derived control currents, and means for applying said combined currents to said transferringmeans. V

2. In combination, two 4electrical transducers adapted to cooperate with a singlel sound record in chronological sequence, a recording l device vprovided With ground noise reduction means,

means for transmitting impulses corresponding to sound Waves from one of said transducers to said recording device, means for independently deriving voltages corresponding to the'venvelope of 'sound impulses from both of said transducing devices, and means for controlling said ground noise reduction means in accordance with said envelope voltages.

3. In combination, two electrical transducers adapted to cooperate with a single sound record in chronological sequence, a recording device provided with ground noise reduction means, means for transmitting impulses from one of said transducers to said recording device, means for independently deriving voltages corresponding to the envelope of sound impulses from both of lsaid transducing devices, and means for controlling said ground noise reduction means in accordance with said envelope voltages.

4. In combination, a plurality oi electrical sound translating devices adapted to cooperate with a sound record in chronological sequence, means for recording impulses corresponding to sound waves from one of said translating devices, means for independently deriving control currents corresponding to the .envelope of sound impulses from both of said translating devices, means for combining said derived control currents, and means for applying said combined currents to said recording means.

5. In combination, a plurality of electrical sound translating devices adapted to cooperate with a sound record in chronological sequence, means for transferring impulses corresponding to sound waves from one of said translating devices, means for independently deriving control voltages corresponding to the envelope of sound impulses from each of said translating devices, means for combining said derived control voltages, means for applying said combined voltages to said transferring means, additional electrical sound translating devices adapted to cooperate with independent sound records, and means for combining their outputs with said impulses corresponding to sound Waves.

6. In combination, two electrical transducers adapted to cooperate with a single sound record in chronological sequence, a recording device provided With ground noise reduction means, means for transmitting impulses from one of said transducers to said recording device, means for independently deriving voltages corresponding to the envelope of sound impulses from both of said transducing devices, means for controlling said ground noise reduction means in accordance with said envelope voltages, additional electrical transducers adapted to cooperate with independent sound records, and means for transmitting impulses therefrom to said recording device.`

7. A rerecording system comprising a plurality of reproducing machines, some of said reproducing machines being provided with means for simultaneously reproducing sound from two longitudinally displaced points on the sound record, means for combining the outputs of said plurality of reproducing devices, means for deriving an envelope voltage from said combined output, additional means for deriving an additional envelope voltage from the secondary reproducing elements, and means comprising a rectiiier element for combining said envelope voltages whereby the combination voltage is equal at any time to the larger of the two envelope voltages.

8. A sound rerecording system comprising a sound record, means for translating said record into electrical impulses, a second means for translating said record into electrical impulses, said second means translating said record at a position spaced from said rst translating means, means for deriving a current corresponding to the average value of said electrical impulses from each of said translating means, a recorder, and means for combining said average value currents before impression on said recorder.

9. A sound rerecording system in accordance with claim 8 in which means are provided for impressing the instantaneous Values of said iinpulses from one of said translating means on said recorder.

EDWARD Wl KELLOGG. 

